Optimizing efficacy and economic benefits of fungicides for peanut disease control via pre-plant analysis of disease risk and irrigation timing
Woodward, Jason E.
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Peanut (Arachis hypogaea L.) is susceptible to infection by numerous foliar and soilborne fungal diseases including early leaf spot (Cercospora arachidicola S. Hori), leaf spot (Cercosporidium personatum (Berk. & M. A. Curtis) Deighton), and southern stem rot (Sclerotium rolfsii Sacc.). Numerous fungicide applications are made each growing season to mitigate losses associated these diseases. Changes to the 2002 Farm Bill resulted in producers receiving approximately 40% less for their commodity, while input costs remain unchanged. With increasing energy costs and suppressed crop value, reductions in input costs are needed if producers are to remain economically competitive. One potential way to reduce costs associated with fungicide inputs would to use an integrated disease management approach. The overall objective of this research was to determine the benefits and feasibility of using reduced input fungicide programs in conjunction with the University of Georgia Fungal Disease Risk Index to maximize profits without compromising yield or disease control. Small and large plot experiments were conducted in fields with varying levels of disease risk. Cultivars with partial resistance to leaf spot and/or stem rot were included in most studies. Yields and grades for these cultivars were equivalent to or greater than Georgia Green, the current commercial standard. Several standard fungicide programs were also compared to their respective reduced programs. Despite increased leaf spot intensity and stem rot incidence for the reduced programs, yields for those programs were generally equal to or greater than their respective standard program. Furthermore, the reduced programs typically provided higher crop values than the standard programs. Bioassays involving S. rolfsii were developed to determine examine fungicide residues peanut foliage and pods. In vitro trials indicated that wounding was not required for lesion development on leaflet or stem tissues. In addition, tissues obtained from the upper canopy were more susceptible to infection by S. rolfsii than tissues obtained from the middle and lower canopy, respectively. This method was successfully used to determine the effect of irrigation timing on the redistribution of foliar applied fungicides. Lesion development on leaflet and stem tissues was greatest when irrigation was applied immediately after the fungicides compared to later irrigation timings. When irrigation was applied after 24 h lesion size did not differ from the non-irrigated controls. Likewise, early leaf spot was more severe when irrigation was administered immediately following the application fungicides, and was significantly reduced for the 6 and 12 h irrigation timings. Maximum leaf spot control was obtained for the 24 h treatment. Conversely, the colonization of pods was lower for the earlier irrigation treatments. The percent pod colonization was similar for all irrigation timings for azoxystrobin and flutolanil; whereas, suppression was greatest for tebuconazole at earlier irrigation timings. This research demonstrates reduced input fungicide programs can be used within an integrated disease management system to adequately control foliar and soilborne ii